Cellular growth factors and growth factor receptors play important regulatory roles in tumor cells and can effect expression of malignant phenotype and biological aggressiveness. Alterations in selected hormone receptors and growth factors of potential clinical importance in breast cancer are the focus of this competitive renewal application. Estrogen receptor (ER) and progesterone receptor (PR) are of prognostic significance in breast cancer and in predicting clinical response to endocrine therapy for women with recurrent disease. Recently, variant ER and PR have been described in breast cancer cell lines and breast cancers suggesting an explanation for ER-positive, PR-positive breast cancers which fail endocrine management. single-strand conformational polymorphism and direct DNA sequencing will be used to identify and characterize alterations in expression of ER and PR genes. Complementary DNA coding for ER and PR will be obtained from normal endometrial mRNA and compared with published sequences obtained from breast carcinoma cell lines to determine if any ER or PR alterations were present in the described cell lines. HER-2/neu proto-oncogene, which codes for a membrane receptor, has been reported to be of prognostic significance in women with node-positive breast cancer. The predictive value of this oncogene in node-negative breast cancer is quite controversial. Since most studies of HER-2/neu expression have been immunohistochemical studies of archival tissue, we will evaluate the antibodies used in these reports to determine their relative sensitivity. Breast cancers from a large cohort of women with node-negative breast cancer will also be assessed for HER-2/neu amplification-overexpression and these results will be compared with disease-free interval and overall survival. With the advent of mammography more women are being diagnosed with breast cancer at an earlier stage and methods of analyzing gene amplification and overexpression in very small samples is needed. Quantitative polymerase chain reaction and fluorescence in situ hybridization will be assessed as methods for evaluating HER-2/neu gene amplification. Immunohistochemistry can be used for evaluating expression in small invasive cancers but in a subjective fashion. Work with computerized image analysis will continue and a technique for reporting immunohistochemical staining as a quantitative result will be developed. It is anticipated that the newly identified human ligand for HER-2/neu, heregulin, will have important biological effects. Heregulin expression will be characterized in normal tissues and breast cancers. The effect of heregulin on DNA content of tumor cells will be evaluated in HER-2/neu engineered cell lines. The long term objective of these investigations is to understand the mechanisms by which hormones and their respective receptors regulate the metabolism of normal and malignant breast cells. This combination of basic investigations is expected to provide new information which will be useful in the clinical management of women with breast cancer.